This is getting worse of late and I think some sort of timing problem may be the fault. I hope it's not worse. about 175K miles on this older Volvo...

I have changed the oil, had new plugs put in and on most trips the car seems like as good as when I got it or better ... (only about a year ago) and seems to have good compression and power.

The pinging or engine knock is like when a poor grade of gas is used ... but I use mid grade gas... not the cheapest and my Volvo usually can go with regular. On a long climb to our local ski resort in late summer (to get cheap season's passes early) I see I have to get my car tuned up in order to make through winter.... I don't relish looking for another car and don't think my car's engine is on it's last legs.)

possible culprits..?? old timing belt needing replacement.... only about 40K on it.. but it's been over 5 years? Electronic ignition.....shouldn't need fixing?

or are my valves fried...? (but I don't use much oil except for small leak in rear seal.... (keeping oil topped off seems to help reduce minor noises ... but this engine knock is reducing performance when climbing hills and pushing on gas ...otherwize in most daily driving (to work and back) I don't notice a problem.

any suggestions for engine "pinging" when stomping on gas? Just old age?