2001 Merc.Grand Marquis "handling" Q plus strange beeping

Two things about my 2001 Grand Marquis; I just purchased an LS with 25,000 miles and took it for a 819 Mile trip this weekend. On the freeway it seemed to take a lot of driver input to keep the car within
the lane.Also it sort of porpoised,that is,the steering was not precise but just sort of launched the front in the desired direction and it can be real twitchy to if you have to make ANY kind of correction.I was really disappointed with the handling on the long freeway runs.It has brand new Michelin's and there is no pull to either side. Is this normal for a 2001? I realize that FORD spent millions to upgrade the steering for 2003.
Also during the trip there was a phantom beeping coming from the dash. There were no accompanying displays on the dash.No doors were ajar. two quick beeps a pause of 1/2 second then two more quick beeps. The tone was higher and softer than the tone made by "select" "reset" etc. Any ideas?
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