Q: I own a 2012 Jeep Grand Cherokee with just under 40,000 miles on it. I've been experiencing a creaking noise while going over uneven surfaces most of the time. A speed bump will not make the noise occur, only bad roads and sometimes very slight bumps. It sounds like it's coming from the driver's side rear of the vehicle. The dealership confirms the noise but cannot pinpoint it. They replaced numerous suspension parts on the left rear but the noise is still present. They have removed panels inside the truck as well but still cannot locate where the noise is coming from. Jeep is sending out a field rep to look and hopefully find and repair my truck. The dealership has had my truck for close to two months.

A: I'm sure it's an annoying noise and apparently you aren't the only Jeep owner with this experience. I found several TSBs in my ALLDATA automotive database addressing this issue. The basic area of focus in the bulletins are the rear shock absorbers. On some models the suggestion is to replace the rear shocks, while others outline a procedure to lubricate the shocks, shock mounts and "bump" rubbers, which are the hard rubber discs mounted on the shaft of the shock to prevent the shock from fully bottoming when the suspension is suddenly compressed over a bump.

An online search also brought up an interesting potential cause for the creak — the parking brake cable housing. Apparently it may be rubbing on a bracket or the body itself.

I've had some success in identifying the source of annoying squeaks/creaks by thoroughly soaking individual rubber suspension parts with aerosol silicone spray. Doing this one bushing at a time, then test driving, may pinpoint the source of the noise.

Q: I was wondering if you could tell me which grade and brands of synthetic oil I should use in my 2010 VW Golf 2.0 diesel engine. Thank you.

A: Some of you may have the same first thought I did; "Hey, that question is too easy." A quick search of VW's recommended lubricants didn't find a simple answer. The motor oil for use in this turbo diesel engine must meet Volkswagen Oil Quality Standard VW 504.00/507.00. VW published a service bulletin with a list of specific 5W-30 motor oils that meet this spec, including Castrol Edge, Pennzoil Platinum VX, Mobil 1 ESP and Valvoline SynPower XL-III.

While VW suggests engine oil and filter changes at 10,000-mile intervals, I'd be more comfortable with 5,000-mile intervals to reduce the possibility of any sludge buildup from oil oxidation. My way of thinking is simply this — oil is cheap, engines aren't.

Q: I own a 2009 Suzuki SX4 Crossover. About two years after I purchased it, an engine light came on which the dealer said was "emissions control evaporative canister lid not sealing tightly." They said it would cost about $1,500 to repair and that it was not of immediate concern. I recently took the car in for an oil change at a local shop instead of the dealership. The mechanic told me I was ruining my catalytic converter by not fixing this and I would need to spend another $1,000 on top of the original estimate if the catalytic converter was ruined.

A: As Al used to say on "Home Improvement," "I don't think so, Tim." The charcoal canister is designed to collect and store fuel vapors from the fuel tank, then deliver them into the induction system when the canister purge valve is activated by the ECM. A leak from the canister would seem to allow some fuel vapor to escape in the atmosphere and might create a small vacuum leak while the purge valve is open. I don't see this creating a significantly lean or rich fuel/air mixture that could damage the converter.

The canister can be tested for leaks by disconnecting the three hoses and blowing air into the No. 3 port.

Paul Brand is the author of "How to Repair Your Car" and "How to Repair Your Truck and SUV," published by Motorbooks.