Engine emitting high pitched whine after EGR cleaning

My 2011 Prius is at 117K miles and I just finished up doing the whole EGR cleaning process and replacing my inverter and ICE coolant. After I got everything buttoned back up (not everything - I've left access to the spark plugs because I'm about to go change those here in a few minutes) the engine area has a high pitched whine, even when the engine is not running. It seems to be coming from the area of the leftmost 1 or 2 fuel injectors. It could be farther down in the engine area, but it's not coming from the left of the engine or the right of the engine or behind the engine or the inverter. It's emanating from the left side of the intake manifold or fuel injectors or something like that. It's a whine like a big electrical whine or something. I've read some other postings about inverters making noises and such, and I don't think that's the source of the noise. I've been driving this Prius for 60K miles and it's *never* made a noise like this. But now the noise is constant as long as the car is on.

Anyone have any ideas of what it could be, what I should check or do? Any help is greatly appreciated!

Is there any way this is related to having the cowl and windshield wiper assembly out of the car? As I said, I've left that stuff out to change my spark plugs real quick, but would like to diagnose this whine before I put everything back together to hopefully prevent having to pull everything apart again.

I'm going to step outside to put in some spark plugs in but I'll check back in shortly.

Quick side note: After I put everything back together the check engine light did come on. It was a P0108 - MAF sensor. I pulled out the air delivery parts and found that the MAF wiring harness wasn't completely plugged in. Put it all back together again, CEL went away, codes still being thrown but my understanding is those will likely go away after I go drive it fast enough for the system to validate the problem is gone. I don't think it's related but thought I'd mention it.

-Michael

 

UPDATE: I got the plugs installed, and reinstalled the various layers above the plugs. I've done some driving and everything seems to be running fine. Still making the noise. Sounds like there's a quiet layer of morse code under the main whine as well.

 

Hi Chapman - Thanks very much for the response. I was starting to get the feeling that it was a "nothing to fret about" given that the driving was going okay and there were no warning lights, but nice to have some confirmation on that, and nice to get a better idea of what's going on. Is there anything to be done about it? Loosening the nuts/bolts on the throttle body? I could definitely be convinced that I overtightened in some places.