Suspecting dying serpentine tensioner, would this work?
 

My car is a 2005, 4 cylinder. (edited to add: Camry)

It is making...what I would poorly describe as a "hollow" rattling sound. Sorry, but that is the only way I can think to describe it. I know it doesn't help.

Noise is RPM related. Engine off, I'm trying to move/rock items in the front by hand to see if something rocks a bit because of a bad bearing. NOthing is moving.

Would this be possible....

Engine off. Remove the belt, leaving it in the engine bay (hopefully not to snag anything). Now, start engine for 10 seconds to verify that nothing is making noise (if I'm right, there should be no rattling)

Now with the belt off, I can rotate by hand, the idler or tensioner parts to see if there is a roughness in their rotation.

It's not easy for me to take it to the shop as my work has me covering a territory (6 different small towns)

How can I conclude that it is a bearing in front without just replacing everything?

I'm mechanically inclined so the aspect of doing it isn't daunting.... it's just narrowing in on the real problem, then finding the time to get it done.

Ok, went out, took belt off. Reached down and this was loose (likely bad internal bearing loose)

What part is this? (I'm guessing not having really dug into it out there that it's the water pump)

If this is the water pump, how much might a dealer charge?

I might have to just let them take it when I'm in town.

Temp gauge is "about" in the middle, never moving. Things work fine so I'm guessing it's moving some water but, if it's dying, which I'm suspecting, I need to get to it.

Car has....guessing...150K on it. I don't recall if the pump has been changed before or not (we bought it new)

That is the water pump.

Don't know costs but this is a standard repair. A dealer or shop should be able to quote a price over the phone given the year, make, model and engine type (4-cylinder).

Pumps do fail. If it is the pump, until repaired keep a close eye on the coolant level in the reservoir tank as the pump bearing/seal can leak.

If you have a hand mirror, you can view the underside of the pump for coolant leakage from a hole in the casting.

You might consider doing this repair yourself to save on transit time and cost. Internet sites like Rockauto and Partsgeek sell high quality aftermarket parts at prices much cheaper then auto repair shops sent to your door.

Pickup up a Haynes service manual or search the internet for videos and other info on replacing this part. The engine is a 2AZ-FE model.

If you are not sure it is the WP, check the belt tensioner which can rattle.

The timing cam chain tensioner can also wear causing a rattling noise.

I'm on the phone now with parts co...might drive into town to get parts and fix tomorrow.

There is a 'cowling' that bolts onto the front of the pump. The belt goes over this cowling (I'm sure that's the wrong name for it)

Anyways, you can wobble the part (with belt off) a bit side to side. I put the belt back on, started car and now that I know where to look, you can actually see a bit of wobble in the cowling as it's running.

Parts place just hung up with me, they have the parts on hand.

Tomorrow's project is starting now it seems!

Have new pump in hand
Have new serpentine belt in hand

On the pump...there is a gasket in the box.

Should I put some sealant on the gasket or put the gasket in dry?

(I was thinking if not a full bead to perhaps put a dab or two to help hold it in place)

This is a question that depends on who you ask. I say no to sealant, just be sure to clean the surface really well. If you remove the water pump and notice that there was sealant used, then it is probably okay to use again, just go easy on the amount.