You don’t need to Whirlpool for extended periods of time nor does the whirlpool need to be very aggressive. That being said large whirlpool amounts and a lot of stirring is not causing cat piss and grass clippings, that all comes down to the quality of your hops (and maybe your water/ph but that’s another matter).
Your beer turning brown has nothing to do with hot side aeration, that’s from oxidation on the cold side and it turning brown means there was a ton of oxygen ingress. Even the smallest amount of o2 exposure (measured in ppb) will have a negative effect on hop flavor and aroma. You need to be incredibly meticulous about keeping o2 exposure to the absolute minimum with hoop beers (or any beer for that matter).
as
@Dgallo said 4mmp is the thiol that causes Cat Piss. At low levels it’s very tropical, at elevated levels it becomes cat piss. This is often associated with hops that are picked at the end of their picking window. As homebrewers we often get what's left over after the pros do selection. The late pick lots that are often more catty, oniony, garlic, diesel are most often what’s left over so that’s what we get sadly.
4mmp doesn’t really survive fermentation all that well and it’s also volatilized by copper so if you’re using a copper CFC or immersion chiller it probably wont make it through to the final beer anyways, at least not much of it. However if your hops are high in it and you DH with those hops the result will be cat piss, onion, diesel, grass, etc.
Smell your hops, of when you open the bag they smell like stuff you don’t want in your beer, don’t add them to your beer, especially on the cold side.
I’ve actually gone to higher whirlpool temps lately. Lower the pH if you want less bitterness extraction.