[b]oil light and buzzer issue[/b]

my sons car was fine till it had a service now this issue with oil light and buzzer .
i thought it was a oil type issue drained , refilled with 20w50, replaced the sensor on the oil filter.
still there, when i put my hand at back of dash and fiddle it quite , or hit hard on the dash is gone for a while then back.
there is no stange engine noise , does not use oil , runs 100% , throught the engine oil filler when idling i can hear the oil splashing around as it should.

will replace the top sensor this afternoon,  this flippen buzzer is driving me crazy.

what else can i do to stop the buzzer pls

regards
deon

I had a similar issue a while back - mine only did it after the car had been stood a while during cold weather. I tried a few things including changing the oil pressure sensor and the circuit board in the clocks:



I finally found it to be the actual speedo head, the grease in there had dried out, I added some white grease and it's been fine ever since. The part I'm referring to is the white plastic bit in the image below:



It's fairly straightforward to remove and dismantle the clocks to get to this. I can't fully understand the reason why it's caused the buzzing/squealing but it fixed it for me.  

now you mention this , when i pull on the speedo cable behind the dash the buzzing stops, dont understanf this one, what does speedo have to do with the buzzer??

From taking it apart I found that the speedo cable drives a magnetic wheel which rotates and the magnetic force then rotates the needle on the gauge. I can only think that the dry grease allowed the spinning magnet to create an electromagnetic field and an electrical charge which caused the buzzing within the clocks.

This was a last ditch attempt for me to solve the problem - I changed the circuit board which made no change, changed the voltage regulator, oil pressure sensor, coolant sensor, oil and filter, checked all the earths etc etc etc and all made no change.

I then bought a full set of clocks and changed over just the speedo head, this solved the buzzing but caused a misread on the speedo reading compared to my sat nav. I then knew the problem was in my original speedo head, it can't be dismantled but I noticed the dry grease so cleaned it and then regreased.

thks will test this weekend want to try anything now
regards

Which bit do I greesy? J