Odd Intake Noise

[dunc12]

Accidentally posted this in the IDI engine forum, apologies 

Hi all, I recently picked up a swapped 1.6TD Jetta coupe. It runs great, fuel turned up a bit and running 12psi with an intercooler. Gets great mileage too (compared to what I'm used to with my 16V GTI).

However, a recent issue has started to concern me. The engine has a cone filter intake on it, just hanging out in the engine bay. I'm starting to get an intermittent "thunk thunk thunk" sound from the filter, sounding like it's occurring once every engine cycle. The noise will come and go, seemingly without any specific condition.

The car doesn't noticeably lose any power while this is happening, but I worry that I have a dying component in the engine. I have yet to perform a compression test.

Is this a common occurrence with these engines? Or is it something I really need to worry about. I can try to capture a video, if it makes diagnosing through the interwebs easier.

Thanks in advance!