Weird sound, scarey sounds followed by even scarier s Options

[pyCube]

Hi everybody... I am a new 914 owner and very much loving it. I found a slick little 1974 2.0 and until recently, all had been good. A few days back I started noticing a very subtle clicky knock sound that really was only audible at low rpm, like at idle. I've been pouring over all the info I could find in an attempt to figure out what was going on, or if I was just being overly paranoid about my new toy. In the meantime, I havent been driving it more than a spin around the block on occasion. Then it happened. I was gonna take it to the store tonight, not more than a mile away, and as I shifted from 1st to 2nd gear, the whole sound/feel of the engine changed. It got very muffled and 'poppy' sounding and it seems to be shaking the car a lot more. Like when I got it home and hopped out of the car with the engine running, it was rather strongly shaking. Other than the freaky sound and big vibration, it "seems" to be ok. I still had power. There was no smoke or leaking of any sort.

Anyone have any ideas on what might be going on? What should I look for when I get the will to go investigate?