Bandit, you have to take off the starter but that's enough to slide the pan back. At that point you could see if the solvents have anything to fight and give it a good manual cleaning. The pump replacement would be simple, and eliminate that question. At 125K it'll appreciate the update.
What I don't like about flushing on high-mile (unknown history) engines is:
1) If there isn't a sludge problem you're just messing up the lubrication ability of the oil. (More of an issue with recent engines.)
2) If there is bad sludge/deposits, breaking them loose for a ride through your engine isn't doing much good. It can be fatal if a chunk gets stuck in an oil passage.
Either way it's shooting in the dark and is causing unnecessary wear. Dropping the pan will tell you what's happening for a couple hour's trouble.
Back to the symptoms...
You said it dropped to zero during normal driving (after warm) and after WOT runs. Was the normal driving on level ground? Where do you fill oil to on the dipstick? I'm thinking possible cavitation/foaming. If it happens again can you stop & pull out the dipstick to check for bubbles?
I'd consider a fresh oil pressure sender & maybe T-ing in an accurate mechanical gauge for comparison. It'd be nice to know if the sounds & pressure are absolutely linked. But you have a better feel for that than I.
So much for shotgun email diagnosis.