Not sure what's going on with my wagon...1992 240 170k. Symptoms over the past 6 months, in the order I noticed them:

1. Rattle underneath the car, very light, Volvo couldn't find anything wrong with the exhaust system when they checked it. Almost sounded like the heatshield, but no, everything seems tight underneath.

2. Intermittendly getting low on coolant in reservoir reservoir but not sure where it's going. No visible leaks, no smoke out the tailpipe that I can tell, no coolant inside cabin or windshield. Doesn't overheat. Topped off reservoir to max (from min) three times in two months, so not a massive loss.

3. Engine is loud, especially when cold. Like a metallic valve noice...tap tap tap tap. Kinda like a Diesel but not quite as thumping, more like a lighter tapping noise.

4. Hot smell from underneath the car. First thought something got stuck on exhaust, but it actually smells like exhaust fumes rather than burned plastic or paper. Then I noticed smoke actually coming from underneath the car, on occasion.

5. Seems to be straining. Not sure if I actually have power loss, if so, it's not noticable, but it seems to strain, especially with that tapping noise, just doesn't feel right.

6. Rattle has now stopped.

I am praying for the cat which is an easy fix aftermarket. Any other suggestions?

I am mechanically challenged so work will be done at a shop, just need to know which shop I should start with.

Thanks guys!