This is probably one of those things that no one else has experienced but I thought I would see if anyone else has heard this noise.

It happens at random. It may not happen for several months then again it may happen a couple times in one week. It seems to happen after braking and coming to a stop but will continue after I stop and go on to move again. I never know how long the noise will continue. It can last for just a couple seconds or up to 10 to 15 seconds but rarely that long. I have tried many things but have found nothing that I can do to make it stop. It just has to stop on its own.

Now to describe the sound. I can only describe it as what I would expect if I took a sharp needle and scraped it slowly across a speaker cone and is somewhat amplified. It seems to come from under the dash but I have yet to pin point exactly where.

The first time it happened it really scared me. I thought something was seriously wrong with the truck because I could not identify the sound. The second time it happened, I was tuned into the sound and realized it was nothing serious. Now, I know it will go away and just ignore it. The first time it happened was when the truck was about 3 or 4 years old. It happens so infrequently that I don't really worry about it and just consider it part of my trucks personality. I am curious though as to what it is.

 

Holy cow. That happend to me this weekend. I thought it was because it has sat for 3 weeks.

 

I get a weird "clunk" sometimes.....only at startup though.

 

I'd check out the power brake booster. If the booster itself is not faulty, it's possible that the push rod adjustment is on the low side of spec. That can sometimes cause a moan under the dash.

 

I have suspected something related to vacuum and specifically the brake booster since it happens during or after brakeing. The brake booster is working as it should with respect to braking enhancement. It is going to be hard to diagnos since it happens so infrequently. I may try to play with the rod adjstment to see if it has any effect on the noise.

The master cylinder was replaced twice by the dealer under warranty. I would expect them to check the rod adjustment during installation but then again that may be too much to expect of a Ford dealership.