Hmm... I would start the links if it only started after you changed those but it could be any number of things truly. Give the engine bay a good look - engine mounts are good? coolant tank isn't loose? you didn't drop a screw driver behind the front quarter panel? lol. (see image below.)

Besides giving everything suspension related a good shake I would check the the following mostly visually/just making sure bolts are tight in this order: Endlinks - Brake calipers aren't loose? - Front sway bar bushing - engine mounts (L/R/transmission.) - lower control arm bushings - strut mounts.

(note: links are for reference images/info. Not trying to make you think you need to do these procedures lol.)

Brake calipers: Give em a good shake, check its bolts. hell, see if you hear the clunk while braking and turning. If you don't hear it while braking it could be because the caliper came loose, was clunking, and doesn't when braking because the brake force secures it. (doesn't conclusively mean its the calipers but something you can very quickly try.)

Endlinks: Make sure they aren't loose at either end.

Front sway bar bushing: You can get a view of them when you remove a tire, should be just behind the steering rack. Volvo C30 Front Subframe Removal | C30 T5 (2008-2013), C30 T5 R-Design (2008-2013) | Pelican Parts DIY Maintenance Article (image 6/7)

engine mounts: open the engine bay, and shine a flashlight by your passenger side engine mount. if you see white crud/leakage it is busted. However this normally results in more vibration not a single "thunk" while turning.
How to Replace a P1 Volvo Engine Mount (C30 S40 V50 C70) (for reference images.)

transmission mount: Make sure the rubber hasn't degraded. if you have the stock mount it will be semi flexible but not the point that it would make contact. Note: The one pictures in this link is a upgraded mount, the oem one is the hexagonal/square edged mount seen at the top. How to Remove & Replace Transmission Torque Mount on a P1 Volvo (C30, S40, V50, C70)

Lower control arm bushings: See first paragraph of this link: Volvo C30 Front Control Arm Replacement (2007-2013) - Pelican Parts DIY Maintenance Article. You can also slightly jack the wheel assembly up a few inches to see if it moves excessively within the bushing. If you do this be very very careful not to accidently lift the car off the stands. you are only trying to compress the suspension a few inches to observe bushing movement.

 

Hmm... I would start the links if it only started after you changed those but it could be any number of things truly. Give the engine bay a good look - engine mounts are good? coolant tank isn't loose? you didn't drop a screw driver behind the front quarter panel? lol. (see image below.)

Besides giving everything suspension related a good shake I would check the the following mostly visually/just making sure bolts are tight in this order: Endlinks - Brake calipers aren't loose? - Front sway bar bushing - engine mounts (L/R/transmission.) - lower control arm bushings - strut mounts.

(note: links are for reference images/info. Not trying to make you think you need to do these procedures lol.)

Brake calipers: Give em a good shake, check its bolts. hell, see if you hear the clunk while braking and turning. If you don't hear it while braking it could be because the caliper came loose, was clunking, and doesn't when braking because the brake force secures it. (doesn't conclusively mean its the calipers but something you can very quickly try.)

Endlinks: Make sure they aren't loose at either end.

Front sway bar bushing: You can get a view of them when you remove a tire, should be just behind the steering rack. Volvo C30 Front Subframe Removal | C30 T5 (2008-2013), C30 T5 R-Design (2008-2013) | Pelican Parts DIY Maintenance Article (image 6/7)

engine mounts: open the engine bay, and shine a flashlight by your passenger side engine mount. if you see white crud/leakage it is busted. However this normally results in more vibration not a single "thunk" while turning.
How to Replace a P1 Volvo Engine Mount (C30 S40 V50 C70) (for reference images.)

transmission mount: Make sure the rubber hasn't degraded. if you have the stock mount it will be semi flexible but not the point that it would make contact. Note: The one pictures in this link is a upgraded mount, the oem one is the hexagonal/square edged mount seen at the top. How to Remove & Replace Transmission Torque Mount on a P1 Volvo (C30, S40, V50, C70)

Lower control arm bushings: See first paragraph of this link: Volvo C30 Front Control Arm Replacement (2007-2013) - Pelican Parts DIY Maintenance Article. You can also slightly jack the wheel assembly up a few inches to see if it moves excessively within the bushing. If you do this be very very careful not to accidently lift the car off the stands. you are only trying to compress the suspension a few inches to observe bushing movement.

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This is excellent. I am going to dive into it today and will report back

 

Was the noise there prior to changing the endlinks out? If not, I'd take a closer look at ensuring those are tightened properly. When I replaced the rear sway bar on my C30 late last year, I thought I had tightened up the links pretty well. Had a lot of noise in the back. Turns out, I did not tighten things well.

 

Do you know the torque spec? I am hoping this is what it is.

 

Perhaps something with a tie rod? That happened to my wife's 2013 XC70 after we hit an interstate pot hole at speed. It was making a similar clunking noise under similar conditions and that turned out to be the case. Not saying this is your problem, but it's what happened to us.

 

Added to the list of things to check!

 

Don't forget sub-frame bushings...

 

Added to the list of things to check!

 

Update: Just needed to tighten my front sway bar links. No more clunking.

I discovered while I was in there however, that I have a pretty significant coolant leak on the front passenger side (same side as the clunking actually). I immediately thought it was the expansion tank, as everything in the wheel well was wet. However, it seems everything is all dry from up top. Any ideas on what that could be? I looked at a few exploded views of the cooling system but couldn't make sense of them.

Also, is the passenger side CV axle supposed to not move laterally? When inspecting for the clunk, I noticed that the driver side CV axle slides laterally pretty smoothly (and is spring loaded of course). The passenger side, does not. Is that normal? The boot also seems to be scrunched inwards on the passenger side as well.

Passenger side CV axle. Also notice all the fluid. That would be a mix of coolant, and oil. But the fresh looking stuff is mostly coolant.

Drivers side CV axle for reference.

 

Update: Just needed to tighten my front sway bar links. No more clunking.

Had a similar experience when I installed the rear sway bar. I couldn't get the damn nuts tightened well enough with my 15mm ratcheting wrench. I'd wager I couldn't done a better job with an open-end socket to really get some torque on it. I just picked up my LCAs at the repair shop today (couldn't get the old bushings out; was more than I had hoped). I suspect when I drop the car off next weekend for alignment the shop will have plenty of bolts I failed to properly torque.

 

Very odd difference in the cvs, if both oe, it looks like the subframe has been moved

 

That's a terrifying thought

 

Your coolant leak seems to be near the water pump. Do you know when the timing belt was done? And are you sure they changed the WP out? (It baffles me that it happens, but it does- ask me how I know )

 

Timing belt was done about 10k (edit: it was actually only 7k miles) miles ago, and water pump was done at the same time (by a reputable independent mechanic while with the previous owner). My own investigation, and the thoughts of some others on the forum lead me to think water pump as well, which is unfortunate as it's so new.

 

It could depend on the water pump that was used. I have seen some fail in less than 10k miles! I was shocked and it cost a customer an engine because it took the timing belt off. I cannot remember the off brand pump but it still looked like it was almost new. I am not saying this is what is going on in your case but does not hurt to look, I only use Aisin pumps because they are OEM and they work reliably.

I would check the hose/line that run from the coolant reservoir to the oil cooler. This is also in the vicinity. Hope you get it straight.

 

Yep, this one is at about 7000 miles. I will give the shop that changed it a call and see if they have any idea what parts they may have used. The shop is one of the most reputable Volvo shops in the country as best I can tell, so I would think they would use good stuff.

I'll check that hose you mentioned when I can. I haven't had the car up off the ground since I first noticed, so I haven't been able to check that one yet.

 

If it is an Aisin pump I would not worry so much but it never hurts to verify.

I posted in your coolant leak post about the cap and reservoir. check this one out also.