Cold start sounds on belt rapping

Does the noise go away after a few seconds?

 

It sounds like the engine knocking problem that plagues Toyotas. If the noise went away but left the check engine light on, you'll need to have that checked, either by the dealer or someone with an OBDII reader and post the code here.

As far as if it's safe to drive, I wouldn't be too worried as they're pretty hardy and will not normally let you do anything to harm the engine. Be sure the oil level is appropriate and have it checked.

 

Here's a thread discussing the cold start knocking:

NEW!!! Service Bulletin for Engine Knocking at Startup T-SB 0012-10 | Page 26 | PriusChat

SCH-I535

 

Already with seeing you say the car is rattling, I can automatically say that is not good and I would be even hesitant to drive it like that, if it is continuous. I would say get the car towed to a shop immediately to get it checked out before other issues start to occur. Please keep in mind if the check engine light is flashing, that this could be a worst case scenario depending on your engine model if it needs to be replaced.

 

Flashing check engine light = replace engine?
Ummmmm... no!
This cold start knock is common in some early Gen III Prius's... see post #5 for the link for the TSB addressing this issue.

 

I've had about 4 engine knocking episodes over the past 2 years with my 2010 Prius (earlier model before the part change per the T-SB-0010-12). Happened again yesterday but louder than previously. I called the dealership to see about getting the intake manifold replaced per the TSB and was told unless the engine knocking happens at the dealership, they won't do it regardless of the TSB and that it is a known defect/issue recognized by Toyota. My car is currently under warranty and I'm worried by the time I could get it to happen at the dealership it will be past warranty. Has anyone else ran into this issue with the dealership and found a way to get them to do it? Thanks!

 

Some have captured it on video and presented it to the dealership.
It's easy to reproduce, so it's easy to capture on video and visit the dealer.

 

Unfortunately it doesn't happen that often for my car (a couple of times a winter) but it sounds horrible. After it happened on Sunday, I started recording each start but of course it hasn't happened again. This dealership told me it would have to happen there for them to hear and run diagnostic codes on which has a slim to no chance of occurring with my car.

 

Go to the dealer on Monday evening- park your car there- make sure no one moves it.
Tues morning or evening (whichever is convenient for you) go there- start your car- only have it run for 1-2 min then turn it off.
Be at the dealership Wed and have them start the car with you present- it will knock!
Of course you need cold temps for the three days too....