[euge]

Autolyzed yeast doesn't necessarily have to give off any sort of a rubber smell. In this case we're concerned with flavor impacts. The flavor is reminiscent of umami or meatlike but in a bad way. IMO this is where  your "muddy" character is originating.

Occam's razor.

[Stevie]

My bet is still the water. Have you checked it with a tds meter?

[mabrungard]

My bet is still the water. Have you checked it with a tds meter?

Exactly. When the OP mentioned "RO", I had to wonder how pure it was. If they aren't using a TDS meter to check the water quality, the whole problem sounds like it could be due to the water.

Another cautionary plea: If you use RO water from any source, be sure to monitor its water quality with a TDS meter. Those meters are cheap and virtually bullet-proof. Get one!

[HoosierBrew]

If you use RO water from any source, be sure to monitor its water quality with a TDS meter. Those meters are cheap and virtually bullet-proof. Get one!

+1. A TDS meter is great, cheap investment.

[qm3k]

Yes! Going with water as the probable culprit. I talked with the owner of one of the newer home brew supply stores in town (I was extremely impressed with his knowledge and his store, but that's another topic). He mentioned that a lot of people in my area were dealing with the same issue, and that RO water from several sources (which I have used) was testing....badly.

He turned me on to where I can get real, reliable RO water. I will also be purchasing a TDS meter  .

Thanks to everyone who responded! I have a very good feeling about my next batch. I'll post a follow-up in a few weeks (re-brewing my most recent dud this week with better water, adjusted properly).

[euge]

Upon rereading I too suspect the RO.   It may be compounded by other factors, but water known/unknowns and known unknowns can be problematic at the very least.

That being said, I have my own RO system (run off the house water softener) that provides nearly pure water. I would not rely on RO stations. Well worth the investment for drinking water at the very least.

My RO TDS ranges from 5-14ppm.

[S. cerevisiae]

Exactly. When the OP mentioned "RO", I had to wonder how pure it was. If they aren't using a TDS meter to check the water quality, the whole problem sounds like it could be due to the water.

+1 

[narcout]

I brew with RO water. My tap water is pretty much liquid dry-wall, so it's not well-suited to brewing. I have made adjustments in the past with Palmer's spreadsheet. I was always successful, for the most part, but I stopped making adjustments when my product began to go south, just in case I was over-adjusting the mineral additions.

Are you brewing with RO water and not adding any minerals back?  Are you checking your mash pH?

[Ready4Launch]

If nothing has changed with your beer or process, then maybe you've changed?  Been to the doctor lately?  Taking any thyroid meds?