Knocking Sound after Head Gasket Repair Becomes Rapid Heard From Interior
 

I had the head gasket done on my 2004 Discovery over the last couple of weeks and with everything back together and up and running, I now have a noise which is best heard from the interior of the vehicle, behind the dash and more so from the middle to drivers side.

The noise starts as a quick knocking sound which then becomes faster and then gets to be very rapid. After becoming rapid it can either stay that way or it will completely stop and then start again after a minute or so of being stopped.

The knocking is not affected by the idle of the engine. It can't really be heard from under the hood when the engine is running nor does it make the sound when the engine is off with the ignition key turned on before starting.

I shifted through the drivetrain to see if there was any affect and at times it seemed to either stop the sound briefly or it sped up the sound. This might just have been a coincidence but I am not certain.

This was not happening before doing the head gasket which I am very sure of - is there something close / next to the firewall that could have been installed incorrectly from the head gasket job that is causing this and if not any ideas on what else it could be?

Update: I have noticed that this rapid knocking sound was fast when first coming to a stop at a light and then slowed after 5-10 seconds of being stopped. Could the idle control motor be making this type of knocking sound? Anyone with good knowledge of the idle motor?

Any thoughts would be appreciated.

Thanks.

Sounds like something is loose and just slamming around.
Oh crap..

That is a slipped liner.
After 10 minutes and a drive about - this gets louder.

When the engine got over heated, it wrecked the head gaskets.
and in your case, may be a slipped liner.

At 2000 RPM the noise should be gone..

You said not affected by RPM. So, then it would not be a slipped liner.
Sounds like a wrench or such left on top of the valley pan gasket maybe.

The sound does not get louder once it starts just faster / more rapid.

The old head gaskets were actually in good shape and did not appear to be leaking. My valley pan gasket was leaking so while there I had the mechanic put new head gaskets in just for peace of mind.

This sound was not there before the recent work was done.

Could be an exhaust leak...

There didn't appear to be any exhaust leaks after the mechanic was done doing the head gaskets and replacing the exhaust gaskets at the same time but I will have a look to see if anything like that is presenting itself.

I am also now wondering if the idle control motor might be doing this.

If it will do this at idle in your driveway, pop the hood and take a yardstick and hold one side to your ear and touch suspect area under the hood. You'l marvel at what you'll hear.

SAI parts? If you have secondary air injection.

Savanah, it is really hard to hear it coming from the engine bay but once or twice I could hear it and it almost seemed like it was from the stepper idle control valve but i'm not totally sure if this could make this sort of knocking / tapping sound(s) or not.

I do have secondary air and the only thing on the drivers side that might make any sounds would be the air control valve but I can't hear anything out of the ordinary coming from that. I don't think there is any other SAI parts on the drivers side other than the solenoid which has bee replaced in the last couple of months.

That is why you want to take a stick to it. Sound travels faster in a solid, and you will hear things from the stick with one ear and from the air with the other. Makes it easy to hear them at the same time. Parts stores sell mechanic stethoscopes too.

If it does it at idle, you could also slip off the serpantine belt to eliminate things that turn. Don't run long enough to over heat.

BTW, the Rover gods frown on beating the stubborn Rover with the stick.

More than likely you have a lose plug wire on your coil pack. Reach your hand back there and make sure all the wires are firmly connected to the coil pack.

View of coil wires without firewall. But I wouldn't describe an arc "tick" as a "knock". May also see it in total darkness.