The beeping is an oil pressure issue. The fill level will have an effect, i.e. if you're low on oil, inertia can cause the oil pump pickup to become un-submerged in the sump during hard cornering, resulting in low oil pressure. If, however it truly is 'random' (i.e. can happen while cruising, cornering, braking, accelerating & everything in between) with no rhyme or reason then it's probably an electrical fault.
Without knowing what engine you've got it's a bit tricky to help, but try checking the oil pressure switch connector. Not sure about VR6s, but I'm pretty sure that all the 4cyl engines have the oil pressure switch screwed into the top of the oil filter bracket on the front of the engine. The one at the front is oil temp (blue), & the one at the back is oil pressure (yellow). Since you're there you might as well do them both - pull the connectors off, & cleanup both female/male parts with scotchbrite/wire wool/wire brush/whatever, then pinch the little returns on the side over a tad more so they grip the spade of the sender/switch better & refit.
If that doesn't work visually trace the oil pressure switch wire back through the engine bay loom to make sure it hasn't chafed on something & split/corroded etc, the connector on the back of the clocks is plugged in correctly & the cable is fine. If you still have issues I recommend:
1) check continuity of wiring
2) swap out oil pressure switch for new/known good one
3) replace instrument cluster with new/known good one
You should be able to get a Y shaped adapter to allow you to fit a proper oil pressure gauge (even if just temporary), along with the original oil pressure switch from somewhere like raceparts.co.uk, demon tweeks etc. This is the only truly reliable way of determining whether you have an oil pressure issure or an electrial issue. Off the top of my head, I think min oil pressure should be something like 30psi (2.1bar).
The Audi Coupe VDO gauge set has an oil pressure gauge in it & they regualarly turn up on eBay for not much moolah - prob worth a punt.
If anyone knows better on any of the above, please correct....!
Benjo