Knocking on the car sound...

[jpapa]

This is happened to me a couple times already. The first time it scared the crap out of me. I started my car up in the parking lot and let it warm up for a couple of minutes. All of a sudden I hear these 3 knocks like somebody was knocking on a part of my car. I looked all around the car and no one was there.
The second time was last night after it was sitting out in the cold for a couple of hours. When I started it, I let it warm up for a couple minutes and then turned on the heater/defroster. A couple seconds later came the knocking again. It wasn't so scary this time, even though I still wasn't expecting it. I can't remember if it happened the first time after I turned on the heat blowers or not. It's just pretty weird because it sounds like something is knocking on the outside of the car. If it keeps on doing this, I'm going to have to take it to the dealership to get it checked out, because it can't be normal. The vents and everything else seem to blow out normal.
I'm just wondering if anyone else has heard this? 3 knocks when cold starting and possibly turning on the heater. Keep the heater off when you turn on the car, wait to turn the heater on after a couple of minutes.

[geokots]

This may sound weird but do you have any large water bottles or anything like that in your car. I swear it happened to me. For almost an entire winter I would hear occasion pops from the car. It sounded like someone threw a rock at it. and it happened usually a few times. A few many months of this happening I figured out that I have a big thick plasic (no the retail bottles) of water sitting on the back floor and it was making the noise. In the cold the air would contract and it would actually suck in a side of the bottle. When it warms up it would pop out and make a loud noise.
I know it sounds stupid but it could be something as simple as that. that same effect could happen with anything; half full bottle of windshield fluid, water bottle or even a part of the car like a loose joint etc.

[XeroState]

Well this is a little off-topic, but in my old car I had a bag of chips in the back seat all winter open (like october to janurary). In Feb I relized it, and me not being one to waste, I try them...they tasted FRESH!!!!...just thought I'd add that in as the story of the bottles in the back seat reminded me...sorry I got off-topic.

[jbaty]

My Redline does the same thing and its not predictable. It sounds like its coming from under the hood but I am not sure yet. If it does not quite im going to take it into the dealership.

[jpapa]

I have a bottle of water in there next to me, but it's definetely not coming from that. It sounds like it's coming from the back somewhere, but that's not for certain. I figure it's something contracting and expanding like that, but I'm just wondering if I'm the only one hearing this. I have no other bottles in the car.

[myredline]

Originally Posted by jpapa

I have a bottle of water in there next to me, but it's definetely not coming from that. It sounds like it's coming from the back somewhere, but that's not for certain. I figure it's something contracting and expanding like that, but I'm just wondering if I'm the only one hearing this. I have no other bottles in the car.

I know excatly what you mean. I have heard it since I have had the car. It sounds like it comes from the rear. I thought it was the exhaust since I had it moved for a body kit. But I have not been able to track it down. And when I took it to the dealer they can never recreate the noise.

[jpapa]

Dealers can never recreate any noises....

[Cole]

Has it happened when you were easing out on the clutch? Someone told me the fuel lines can knock sometimes. I've had knocking from the passenger rear but only when I'm easing into it from a dead stop.

[jpapa]

I wasn't pressing in the clutch or driving it, it's when I first start the car up. I tried to make it happen again just now by turning the heat on after a couple minutes, but it didn't happen. So it doesn't happen every time, but it sounds like other people hear the same thing I'm hearing. I don't know if this is a good or bad thing.

[johnboy8221]

it happend to me a couple of times my theory is it has something to do with the exaust heating up the original muffler because after i've put my aftermarket one on it hasn't done it