strange pumpish sound

[gunther_01]

So my truck has plenty of issues, but here is a new one to add to the list. An occassional pumping like sound and associated feel coming from the firewall/under cab area. Since I think I have a failing drivline speed sensor, I'm thinking maybe its the ABS pump. The sound is refined, like whatever it is is suppsed to work that way. But it deffinatly a motor of some kind. I'm not using 4x4 so I would assume its not the transfer case motor..

Just wonderin if this has happened to anyone, and maybe some pointers on how to resolve it.

[fordmasterdieseltech]

sounds like possiblyy your vacuum pump your hearing.

[gunther_01]

I don't think so..not the little pump on the passenger fender if you mean that one?..I can hear this one driving down the road, and feel it in the foot pedals (not surging ABS style) and in the steering wheel. Just a smooth but very noticable pumping like sound.. a motor oof some sort. A Wheeeeee, but with some power behind it. Like an electric hydrolic pump.