Noise under the hood

My son has a 2002 Honda Civic, 4 cyl, manual trans, front wheel drive, 110K mi.

There is a random extremely loud thud-like noise coming from under the hood that sounds like someone hitting the car with a sledge hammer and can be felt in the steering wheel and in the gear shift knob. The thudding happens occasionally when first starting up the car but mostly starts happening after driving it after 10 minutes or so. The thudding occurs both while driving and when stopped (at stop lights for example.) The thudding doesn’t increase in frequency with an increase in speed. The noise is so loud that it sounds like everything under the hood will fall out. On rare occasions it can be driven for 30 minutes or so around town without making any noise, most times however it will eventually start maiking noise. I’ve replaced the struts which were leaking but the noise still occurs.

Any clues or suggestions what could be the problem? Thanks.

I’m thinking you may have a broken motor mount and what you’re hearing is literally the engine hitting something as it rocks.