Loud engine knocking sound
 

I just picked up my first boxster yesterday, an 01 S with 61k miles. While driving it back I started to hear a clicking sound a couple hours in that proceeded to get louder. It now sounds more like a loud knocking sound. As far as I can tell it has nothing to do with rpm and putting in the clutch doesn't change anything. If I put my hand on the e-brake I can feel the pulsing vibration, if that makes sense. As I sit in the drivers seat it sounds the loudest from my back right. Engine performance is just fine and I can't feel anything else wrong.

Any ideas at what I might be looking at?

Could be anything except a good thing. Someone has to get under the car & pinpoint where the noise is coming from. Hopefully it is not coming from the engine. The parking brake shoes are inside the rear rotors. This may be causing the vibration from the park brake lever. If the noise is coming from the engine running it may increase damage.

As BYprodriver suggests, get under the car and take a look. Be sure to check the engine and transmission mounts.

Check heat shields around cats.

Engine compartment fan?

Got a CEL? If you're in the SLC area my shop is 1700S and 900W and I'm glad to read any codes or help look if you need a hand.

Good luck with this. Hope it's something bolt-on!

Sounds like seller's gum fell off!

Just a guess, E-brake cable rubbing on the inside edge of the wheel. The knocking comes from it hitting some wheel weights.