Hey guys. I have a 1994 Chevy Blazer (Full Size) with the 350 TBI, and I'm hearing some odd noises coming from under the engine compartment area, possibly under the truck. Here's the deal. It has had the glorious valve ticking for awhile now, as it is a bit old (200K miles now), but this noise is new, and bear with me as I do my best to describe it. I hear a metallic scratching noise, kinda like a cross between dropping some finishing nails into a coffee can and the sparking noise that comes off of a welder (sorry, that's the best description I can do). I wouldn't call it a faint noise, but it wouldn't be loud enough to catch on tape, or I'd try. It is pretty inconsistent, but it only seems to happen when a drive gear is engaged. Speed and acceleration rates don't seem to matter, but I haven't tested this enough to be certain.

My question is, what can I check before I take this thing in and get raped by a repair shop? I looked up the symptoms and it sounded like it could be the drive shaft, if that makes sense. Anyway, thanks for any help you all can give me. I know my car pretty well, but these trucks are just different enough to confuse me.