I want to identify a flavour I have had in a few of my pale ales (half
mash).

What I don't know:

My palate and my ability to describe flavours is poor in the extreme, so
I know I am not helping myself by not being able to compare it to something.

I can't really identify the flavour from the descriptions in various
books/ web sites (eg howtobrew.com), although I'll admit I don't know
what horse sweat smells or tastes like.

What I do know:

I know from extensive research :-) in England and Scotland (and here in
New Zealand) that this isn't a flavour that is normally present in pale
ales. However, I have found this flavour in many Belgian ales -
although from slightly less extensive research :-(

The flavour was not present when the beer was very young (only two weeks
after bottling), but has developed after the four - six weeks point.

Any help appreciated.

Cheers
Robert