High Pitched whistling noise and fluctuating oil pressure

I noticed about a week ago that my 2000 XJ was making a high pitched whistling noise in the mornings on my way to school, and at night from my way back from work.

I only notice it when it's cold outside and at first it seemed to be related to whether or not I was running the heat.

Tonight I noticed that the oil pressure would fluctuate between one notch under 40 when I let it coast, to 1 notch above 40 when I was accelerating.

Whenever I let it coast and it went under the whistling would get louder, but whenever it got above 40 the whistling would disappear.

So I was wondering what the cause of this could be and if I should get it taken care of as soon as possible.

Thanks a bunch.

The whistle is most likely a vacuum leak....

Have you noticed an increase in brake pressure needed to stop? If so, brake booster. Otherwise, you are just going to have to find the leak the hard way.

Fix the vac leak first...I don't think the oil pres is an issue.

2nd repost?