2005 Prius Mystery Noise

[QUOTE=Houston;1159014]on startup my 2005 Prius standard produces a low level cyclic noise which sounds like a hacksaw. This noise lasts for several minutes and is not affected by putting the car in motion or leaving it parked. The noise seems to be coming from the Synergy Unit but who knows? Any suggestions??[/QUOTE]

I would first check out the electrical powered coolant pumps near the driver's side headlight, remove the plastic engine cover and try to feel/listen to exactly where the noise is coming from.

 

The pump behind the headlight is the pump for the cabin heater. It is not terribly difficult to change this yourself. There is another pump on the storage tank just to the left of that pump in the fender well. That pump is the subject of a TSB. You car may be out of warranty though. You can see that info here:
http://priuschat.com/forums/toyota-...-you-have-squeaky-chs-water-pump-new-tsb.html

 

RE my last post---I tried again and the sawing noise is coming from the pump[?] unit directly behind the left headlamp. Can you tell me what this unit is and should I worry???[/QUOTE]

Sounds like the inverter coolant pump, very important especially in hot weather with a/c use, sounds like yours should be replaced.

http://priuschat.com/forums/gen-ii-...g/36513-inverter-coolant-pump-takes-dive.html

Here is one link to a priuschat discussion, 13 pages worth, I don't want to try to summarize.

Also how to replace with some photo's
http://priuschat.com/forums/gen-ii-.../65173-how-replace-inverter-coolant-pump.html