My parents complain of the same thing when they come round my house
(Volvo S80). I remember reading an article that blamed 3G phone masts
for this affecting a whole village somewhere in England, but the telcos
denied it.

The problem is that newer cars tend to have remotes working on
433.92MHz. This is an unprotected frequency used by many remote link
devices (e.g. wireless thermometers for clocks/weather units that show
inside and outside temperature), and also by relatively high power users
such as amateur radio voice repeaters and the MoD (some bright spark
thought it was a good idea to allow low power telemetry stuff like this
in the middle of the long standing 70cm (430-440MHz) amateur radio band,
and not even put it to one side of the band but use a frequency in the
middle of the relatively heavily used voice repeater section!).

Worse than that, the receivers for car remotes are typically cheap and
nasty pieces of work, so a local high power transmission that isn't
particularly close in frequency can cause desensitisation of the
receiver (imagine a friend trying to talk to you whilst someone standing
next to him is shouting).

Possibly the easiest way to find out what is causing the interference is
to find a local radio amateur with some 70cm equipment, who should be
able to help trace where it is coming from. If it is a constant problem,
I'd think it is more likely to be some telemetry device (like the
weather station things or a wireless burglar alarm) than an amateur
repeater, as the repeaters typically aren't in use 24 hours a day (they
only transmit when people are talking through them). If you are close to
a commercial premises, they may have something in use that is causing
the problem.

Matt

Yup - its called an open public frequency. That means you get to share
it with cordless phones, baby monitors, house alarms etc etc.

You may think I am taking the piss but try this: Facing the car, stick the
key in your ear, open your mouth and press the lock/unlock button. Your head
concentrates and directs the signal at the car.

Originally I assumed I was a freak until I saw Jeremy Clarkson do it as
well! Clarkson - I suppose we could all be freaks together??!!

The other option is to find where the receiver is (usually middle of the
windscreen) and put the key near it and press.