Dear Car Talk:

Could you address the use of oil additives? I am particularly interested in one called System 48, because I inherited a case of it from my father. Should I dispose of it, or is it OK to use? I have a 2007 Infiniti G35 with 345,000 miles, a 2010 Hyundai Santa Fe with 148,000 miles and a 2014 Ram 1500 with 105,000 miles. — Tim

Gee, Tim. I hope he also left you something of actual value, like a fountain pen.

First of all, if you’ve got a car with 345,000 miles on it, for crying out loud, don’t add anything to it. Whatever you’re doing is working. You’re probably driving gently, changing the oil regularly and keeping up on regular maintenance. Good for you.

I’ve actually never heard of System 48. But in my opinion, oil technology is so good now that you’d have a hard time convincing me that any oil additive is necessary in 2022.

Any full-synthetic oil on the market now will do a spectacular job of lubricating your engine parts. And most can be used for 10,000 miles before they need to be changed. Even standard, deaddinosaur-based oil is better than ever before and will do a fine job if you change it as recommended.

There are various goops and potions that are sold to desperate people whose cars are on their last legs. Those folks are willing to try anything that costs less than $30 and promises to save their engine. But I don’t recommend any of those products. And neither do the engineers who designed your car, by the way.

So despite the sentimental value of your inheritance, Tim, I’d put the case of System 48 on eBay. Then, with the proceeds, buy yourself a nice pen to remember Dad by.

Dear Car Talk:

I have a 2011 Toyota RAV4 with about 95,000 miles on it. Recently, I noticed that when I get to about 40 mph, the car makes a weird rattling or loudish whirring sound. It sounds like it is coming from just in front of the front seat area of the car. If I hit the gas hard or take my foot off the gas, the noise stops.

I’m hoping you can help me figure this out. I tried taking it to a mechanic, but since they aren’t getting an error message on their computer,

they don’t know what it could be. Thank you! — Edie

You’ve given me several excellent hints here, Edie. If only I was smart enough to make sense of them.

Actually, I think your noise is related to the exhaust system.

My first guess would be that a heat shield around your catalytic converter is loose and that’s what’s rattling.

Why do I think that? Well, first, since there’s no warning light or computer code, that suggests to me that it’s not an engine issue.

Second, rattling exhaust systems are often sympathetic vibrations. That doesn’t mean they feel sorry for you when they vibrate. It means that they vibrate because something nearby is vibrating at just the right frequency to set them off. And these sympathetic vibrations in cars often happen only at specific speeds.

Third, your catalytic converter is located just in front of the passenger seat, under the car — right where you say the noise is coming from.

It’s possible that it’s not the converter’s heat shields. It could be a loose or broken honeycomb inside the converter or some other part of the exhaust system has come loose

or is touching something it shouldn’t be. But the heat shields are the first thing I’d look at because that’s very common.

If you can get your mechanic interested enough, I’d strongly suggest he take a test drive with you and hear the noise for himself. First, it’ll allow him to rule out anything dangerous. Second, once he hears the noise and where it’s coming from, he’ll probably know exactly what to do.

If he can’t identify it during a test drive, he can always put the car up on the lift while someone else stays inside it. The driver can then rev the engine to different speeds and try to make the noise occur.

If they can get it to make the noise on the lift, the mechanic under the car should be able to find the cause in a matter of seconds.

Even if he can’t duplicate the noise, he may be able to find something under the car that’s obviously loose or not connected as it should be. And if he fixes that, there’s a good chance that’ll make the noise go away ... along with a few bucks from your bank account. Good luck, Edie.

Got a question about cars? Write to Ray in care of King Features, 628 Virginia Drive, Orlando, FL 32803, or email by visiting the Car Talk website at www.cartalk.com.