Clunking sound under the hood???

Hey guys,
This just started about a week ago, when I'm drving slowly in a parking lot for example, I hear this annoying clunking sound but it seems like its coming from under the hood, not the suspension, almost like something hitting the firewall or K-member. So I was thinking maybe the motor mounts were on their way out, but I don't really hear anything when I just rev the motor or if I hammer it and bang through the gears on smooth pavement. Can bumps in the road actually make a worn engine mount clunk? I can't see what else it could be. I installed new struts last friday and inspected all front-end components and everything looked tight as far as the sway bar, balljoints and tie rod ends, and the sound started a few days before that. Also sometimes it seems like I can feel the clunk in the clutch pedal, but not the brake or steerign wheel.
How do yo guys check you engine mounts?
Thanks for any input.

Stock C/C plates. The headers did look like they came close to the steering shaft but wouldn't I feel it hitting through the steering wheel if that were the case? I don't feel anything unusual through the steering wheel. I'll have a closer look at that, but I think they clear it fine. I'll also check for the front control arm bushings as well as the K-member bolts next time I'm under there, but I won't have time until next tuesday. I only did however only notice it after I did the headers. Maybe it just wasn't that liud before that. Thanks for the tips guys. I'm sure I'll find the culprit one way or another.