The Mégane II Owners' Club

Bass is non-directional so you will definitely hear / feel it in the boot if it's of sufficient size and appropriately powered.

Have you checked the alternator charge rate and the alternator regulator?

Yes, change the alternator belt and the water pump as well.

When was the transmission fluid last changed and the transmission serviced?

Check that none of the roof lining clips have come loose.

I was going to say it was the tappets but you say it also makes the noise with the engine off?

Focal are a reputable car audio brand.

Which model of speakers are you getting?

Check that none of the roof lining clips have come loose.

Get the relays or starter motor looked at.

Can't see why it wouldn't be covered under warranty.

Good to hear you stood your ground with the dealer.