Symptoms of a bad ABS pump?

[cshields]

Hi there! This is my first time posting to this forum, but I have relied on it in the past to trouble shoot problems with my X5, so many thanks to those of you who unknowingly helped me in the past.

I have a 2004 3.0L X5 and am having a problem with the brakes. When I brake firmly I'm getting a momentary dull grinding noise that I can feel in the pedal. It happens at speeds as low as 25mph. If I brake gently all is well. This problem appeared yesterday for the first time, but is the latest problem in a week of problems.

Here's the background: last week I was in southern california. The car was due for new front pads and rotors. Took it to our beloved, trusted mechanic who has serviced it for years. He replaced the pads and rotors. After he took it off the lift the auto leveling suspension was misbehaving but not giving a fault code. He recalibrated it, but it still wouldn't level. After the car sat for 1.5 hours it leveled itself and seemed to be fine.

I drove to northern california the next morning. On the drive we noticed the ABS kicked in a couple of times when it ordinarily wouldn't. The suspension started to act up again, and was sitting low on the passenger front corner.

I took it to a mechanic in northern california. They found a loose bolt in the front passenger side lower control arm and tightened it. This seems to have fixed the suspension leveling issue, but the following day the grinding noise while braking popped up. I took it back to the mechanic, who test drove it and said it was the ABS going off. Mind you, this is not the rhythmic pulsing you typically feel when the ABS kicks in. This is the sort of dull grinding that makes you wince when you hear it because it sounds like a lot of money draining out of your bank account. The mechanic thinks it may be the ABS pump but wants to do some more testing before replacing that part.

There are no warning lights on the dash, and no codes in the computer to indicate a problem.

So...what are the symptoms of a bad ABS pump? These problems are driving me crazy...I welcome any and all input!