Mine randomly increases/decreases in volume, regardless of the "urgency" level (speed of beeps). It usually starts out loud, then will suddenly go very quiet, then back to loud sometimes.
I know it does this with top up - don't recall if it does with top down.
I'll have it checked out at my 5,000 mile service. That'll probably be another 5-6 months though. I'm trying to save the Eos from parking lots as much as possible, driving my old Pontiac GTP unless it is a pleasure cruise.