Puzzled - "Humming" Noise Under Bed?

Okay...I know I'm not crazy (yet), but something has me totally mystified.

Yesterday, my wife called me out to the garage and said, "there's something humming under the bed of your truck...sounds like there's a small motor running".

I thought SHE was crazy, but when I walked by the fuel lid, I heard it clearly. Got under the bed (vacinity of the rear axle) and something "motor like" was definitely making a humming noise. The engine was off and it hadn't been running in over 24 hours.

It stopped shortly after I got my face under the chassis, but my wife said she's heard it a few times before she finally brought it to my attention.

What the heck is/was that? 2009 Tacoma Sport Ext Cab, 4.0L.

TIA!

 

Fuel pump if I recall. Keeps the lines primed.

 

start from the simplest on up.
My pops had a wierd banging/knocking noise when he turned corners.
Turned out he had a loose hitch ball under the seat.

 

probably the fuel pump. The trucks do a self diagnostic check or something like that a few hours after you shut it off.

 

Key off Emmisions tests. Self checks etc.
Normal.
You can sleep well. It's all good..

 

Y'all are the absolute best!

I actually thought about "huh...could it be the fuel pump??" Not being a wrench at all, I had no clue about any type of self-diagnostics. I was going to ask if it could be the fuel pump on the original post, but I figured I'd come out looking more stupid if that had nothing to do it the noise.

I have to keep reminding myself to come and post more often, or at least read more....this is the best forum by far.

I really appreciate the input, and I can now cancel my appointment with our city's psych facility.

 

I just had this happen to me this morning. Humming noise coming from under the truck. Def sounds like a elec motor. The truck had been off the whole night. I heard the noise when I went into the garage. I turned the key to on position and then turned off without starting the truck and the noise stopped. I hope this self diagnostic stuff is all that is going on. I was worried until I found this thread. Has anyone else noticed this happening on their truck?

 

I guess I was. Worried because I just did the yellow wire mod yesterday. Lol

Anyone else notice this happen to them when their truck was off and parked for some time?

 

Bump......No one had this happen to them? I noticed this because I just happened to walk in while the humming noise was going on. I don't know how long it was actually doing it though.

 

if you hear it again,loosen your gas cap...if it stops the evaportive system is venting out pressure

 

I had the exact thing happen Christmas day -- truck had been shut off in the garage for over 24 hrs - - I turned the truck to "on" and then back off -- noise stopped.

 

I heard this too a few months ago. Scared me. I had just recently purchased the truck and thought something was wrong. Then I read its a self test.

 

I'm glad to know that this seems like a common thing. I thought I jacked something up doing the yellow wire mod. Thanks for the replies guys.

 

It is the Evaporative Emissions Self test, it is a 2 trip key off self test automatically ran after a few hours after shut down.

 

Mine ran this 9-10 hours after shutdown.

 

totally normal, read the manual.

 

Search!

http://www.tacomaworld.com/forum/2nd-gen-tacomas/308857-wtf-sound-rear-end-truck-off.html

 

I heard it the other day and it freaked me out haha. Glad it's normal.

 

"Search", what a concept!

That's how found this old thread. It was the first one to come up.

Now I can rest easy when I hear it. This was the second time it was noticed.

Does anyone have any idea how long this, "self test", takes?
I searched that also but didn't find anything.

Thanks

.

 

Yep. And all Toyotas do it....even my wife's Prius. I actually walked out to the garage once and both were humming away