We have an 2003 E320 with 65K miles and while we were on the interstate yesterday an alarm went off that sounded like a cell phone english siren.

It came from under the hood, but sounded like it was all over the car. It came on while driving about 65 and sounded for about 15 seconds and quit. Before we could safely pull over stop on the side, it happened four times.
It sounded as I got out to raise the hood, but quit.

There were no errors on the dash screen and no problem developed.

I looked through the manual and found nothing like this alarm sound.

Any ideas where it came from and what it was for.

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1998 Land Rover Range Rover 66K Miles
1988 300SE Totaled in 1998, hit by drunk driver, but we walked away OK
1989 420SEL 140,000, just warming up. Total by 18 wheel gas truck rear ended, but refused to lose another MB. Had it repaired cost $10,000+ Great Car again SOLD it for a 2003 C320 to save on gas
1991 2500 Suburban 454, 130,000, Best truck in the world. SOLD it out right.
1952 8N Tractor 1,000,000-/+

It might be a add on aftermarket alarm, look around for a speaker. Factory alarms usually use the horn / exterior lights.

If it is aftermarket, be sure to use care and remove all wires and repair the factory wires.

I also wanted to say that the siren sound was not coming from the horn.

It stopped before I could locate it but it was coming from under my hood.

But if it was an aftermarket alarm, why go off at 65 on the interstate?

We bought the car preowned from the MB dealer, and the dealer is the only servicing company, we have the records. The car was maintained expertly.

I love a good mystery but not on the interstate in rush hour traffic.

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1998 Land Rover Range Rover 66K Miles
1988 300SE Totaled in 1998, hit by drunk driver, but we walked away OK
1989 420SEL 140,000, just warming up. Total by 18 wheel gas truck rear ended, but refused to lose another MB. Had it repaired cost $10,000+ Great Car again SOLD it for a 2003 C320 to save on gas
1991 2500 Suburban 454, 130,000, Best truck in the world. SOLD it out right.
1952 8N Tractor 1,000,000-/+