1999 4.0 XJ.
Muffler has been loud and rattling for a few years now, guess the muffler bearings are going bad. One of the things the previous owner did was add a all stainless steel exhaust that measures 2.5" at the OD, not sure if this is standard OD or not.

I drive the jeep about 6k miles per year and am looking for muffler replacement suggestions, something not load and not so restricted it will lower my mpg.

Suggestions?

What muffler is on the vehicle now?

Need to know to recommend muffler of the proper length and in/out configuration

My best recommendation would be a Flowmaster 50. Not loud, but mellow in the power band. Sounds great at idle or just cruising below 40, then you can barely hear it driving down the road. You can buy them in any configuation for inlet and outlet size or centered or offset. They are heavy gauge metal and never change tone since they are just baffled with no packing. If you want loud, Flowmaster 40. The only problem is length. They are short and may need extensions to fit. It's the closest to that V8 sound you'll ever get from a 4.0. I have mine welded in with an extra hanger because they are heavy.

Took a quick look at the muffler today, I can see a couple of small rust holes. Decided to drive to the local muffler shop and was told I have a stock muffler, so I assume the rusted out holes and loose baffles are the source of excess noise.

Since this is a street jeep my first thought is just replace with another stock muffler, unless you guys can talk my out of it.

I can tell you of my experience with the Walker "stainless" muffler and other "stainless" components. They fit fine, and sound like stock, but a magnet sticks to them all, and the color turns to rust in a matter of months with no road salt. The exhaust has been on the car for ~2 years, has not rusted out yet, but will not last a decade or anything like that.

Most stainless just contains elements that improve it's ability to resist rust, but don't stop it. If a magnet sticks to it, it's got enough iron in it that it will rust. I just may take longer. Think refrigerator! Appliances with stainless surfaces or even kitchen knives will rust easily if left submerged in water long enough. Mufflers used on aircraft are expensive, but last VERY long. You don't want to know how much they cost!

A cheap stock muffler will usually last about 2 years. With Flowmasters, the pipes will rust out before the mufflers will.

So, I have to ask those that have experience with a stock sounding or near to stock sounding mufflers, what have you installed that will last 5+ years?

The local shop quoted me $100.00 for a stock type muffler installed. Looking on Carid a low cost muffler can be had for as low as $22.00, I don't mind spending more for increased life.

Walker quiet flow has a nice mellow sound. Just a tad louder than stock. I got a few years before selling the jeep without issue. I tried a number of mufflers trying to get a decent sound. Thrush welded (good flowmaster clone), glasspack/cherry bomb etc. Walker by far was the best.

I’ve used Walker in the past on a previous XJ. Can concur it turned brownish in about a years time, wasn’t fully rusted though. The sounds and performance seemed the same as stock to me, maybe a tad louder. Getting ready to put a Walker complete exhaust kit on my current XJ. It has what appears to be the factory muffler (can see the Chrysler logo on it) almost completely rusted through.

Well, it does not have to be this way. Stainless hardware from a run of the mill hardware store does not rust when I put it on my kayaks, despite regular exposure to salt water. And magnets don't stick to that. Stock exhaust lasted 15 years on the jeep which I bought new. Stock exhaust lasted almost 20 years on my Volvo 240, and then the replacement (Starla) lasted 10. There are a number of stainless exhaust sets out there advertised for ~$500, which I would gladly pay if I knew the set would last 10 years. Like https://www.quadratec.com/products/77603_802_07.htm.

Anyone with any experience with something that actually lasts?

As I said, there are many grades of stainless. Each of them have different qualities and purposes. The one I'm most familiar with is 303 because it doesn't rust and is free machining. It's used mostly for structural parts that have to be drilled or threaded and doesn't rust. The key is it's non-magnetic. This particular grade is hard to make in thin sheets that can be formed into stuff like mufflers and pipes, however. I've used it to make couplings for marine driveshafts and deck hardware. It's not good for knives or cutting tools because it won't hold an edge well. The best chef's knives were carbon steel until ceramics came to be, but they need exquisite care because they rust very easily.

Some grades weld easily, some don't weld at all. I've had problems with stainless bolts screwed into aluminum in the presence of chlorinated pool water that corroded badly and locked in place so badly they had to be ground down flush and moved to another location. These were 303 stainless threaded in 6061-T6 aluminum.