Popping or tapping sound

[packmule1911]

Lately there is an inconsistent audible "pop" or "tap" sound coming from the front of the car. The tap sound like someone lightly tapping with a small hammer. It could sound like a pop as well, kind of the pressure valve releasing, or something under tension releasing. It's not loud exactly, but it's annoying and I hate having a sound within ear shot whose cause isn't known.

Sometimes it will do it at idle and be like pop (2 seconds) pop (2 seconds) pop (2 seconds). Other times there might be more or less space between pops and/or a different number of them. It's not consistent in how many sounds happen, the tempo, etc. The sound is always the same pitch, volume, and duration. Of course it doesn't do this when I'm trying to listen under the hood. I expect it might be making them when driving too but there's a lot to drown them out then.

The only things done around the front end are:

* front sway bar bushings
* front sway bar link rebuild kits
* removal, cleaning, and reinstallation of the IAC
* oil change
* rebuilt front axle 12/9 but the sound was there before that
* new front wheel bearing/hub assemblies
* front brake caliper pins removed, cleans, greased and re-installed

None of this stuff seems like it would cause an intermittent pop or tap sound from the front.

This is driving me nuts. Thanks for any suggestions you can give.