I think you are self MIS-Diagnosing green beer. You are tasting possibly an off flavor, but since you are tasting it pre bottle conditioning (minimum 3 weeks at 70 degree.)
Betcha when you come back to your beer at 4 weeks or so, you won't notice a thing.
The only way you could possible have stressed yeast enough to autolyze in three weeks would be if you perhaps were using fifth or sixth generation unwashed and pitched on top yeast.
People have sat their beer on the yeast cake for 6 months and not had any problems. Autolysis is largely a bogeyman for the homebrewer, and if you go back and re-read John Palmer's "terrifying to the new brewer" passage in How to Brew, that every new brewer panics about, you will notice a couple things;
1) He is actually talking about
Lagers as being susceptible to autolysis. That is because, when you are making a lager, you are LAGERING or storing your beer for a few months to cold condition. ANd you are making a beer where any perceived flaw stands out since there is virtually no dark malt or even hop presence. If you are attempting to sit a really light beer on a yeast cake for months and months,
you would possibly have autolysis occuring, but we're talking MONTHS. So that's why you secondary a lager, you take it off the yeast and store it.
2) John Palmer ends the section in HTB with this caveat, which MOST new brewers seem to miss, probably because they are already in beer is gonna be ruined panic mode.
....As a final note on this subject, I should mention that by brewing with healthy yeast in a well-prepared wort, many experienced brewers, myself included, have been able to leave a beer in the primary fermenter for several months without any evidence of autolysis.
And furthermore he says this.
Leaving an ale beer in the primary fermentor for a total of 2-3 weeks (instead of just the one week most kits recommend), will provide time for the conditioning reactions and improve the beer. This extra time will also let more sediment settle out before bottling, resulting in a clearer beer and easier pouring. And, three weeks in the primary fermentor is usually not enough time for off-flavors to occur.
So again I really really really don't think you are experiencing autolysis, since it is nearly impossible to have it happen in only three week.
More than likely, like I mentioned earlier, you are simply experiencing a green beer taste, no matter how odd it may taste. That's why I don't recommend anyone worrying about a flavor they perceive in primary or secondary, because your beer still has a journey to go through in the bottle...The race isn't over until it has bottle conditioned.
Read my blog
On Patience & Bottle Conditioning for more info on the process.
I firmly believe that you won't notice the flavor in 4-6 weeks.