Front suspension clunk over bumps
 

I have recently received my 04 WRX from a shop which rebuilt my engine (it also changed front brakes for legacy spec b setup and mounted backing plates on my 5speed gearbox). I din't have the car for a couple of months. I hoped that I wouldn't have to do anything with the car for a while, but now I started hearing knock/clunk from the front suspension. The knock seems to come from left frond end. It's not metallic, it seems like something hitting a floor.
The knock is rare, it can be heard only in couple of situations:
with slow speeds:
- going over a steep speed bump - the single knock can be heard just after leaving the bump (not when hitting it), so probabply in the moment of big decompression or just after that; I also think that I can only hear it on short speed bumps, not the longer ones, for example:
/T\ - knock /TTTTTTTTTTTTTT\ - no knock
- turning left and hitting a low kerb (for example turning left from a road into a yard) - single knock;
So - immediate compression and decompression seems to cause the clunk, while compression only or decompression only is not strong enough.

- with road speeds it can be heard when taking right turns (weight transfer to the left) over noticeably bumpy bends; usually it's also single clunk, but the number of clunks increases together with speed and size of potholes (up to 2-3); sometimes it sounds like my left strut is going to jump through my bonnet.

Since I didn't have my car for a couple of months, I can't be sure if the clunk wasn't there before engine rebuilt and front brakes swap.

Swaybar endlinks and ball joints are fresh (less than 5000 miles). Steering rack was swapped for a second hand STI rack and stock struts were swapped for refurbed (regreased, painted) STI WR1 struts also less than 5k miles ago. I think that I didn't hear any clunk after swapping them.
My suspension was checked during MOT couple of days ago and they didn't find any play, the technician said it is exceptionally stiff.
Because struts were regreased, I tried to tighten all bolts on my front struts. All of the top bolts on both of them were very tight. I managed to turn bottom nut on the left front strut by a quarter of turn, but it didn't help.

Could any of the last repairs cause this kind of knock? (removing and mounting engine, removing and mounitng gearbox, swapping brake calipers)?
Any ideas what to check to find the cause?

if the brake calipers are bigger then there could be clearance issues. on standard 17" wheels, but im no expert so it could be something completely different