I had this problem on my G- it was a loose front control arm- made that metallic squeak sounded like it was in the dash.

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Ron
Current Sports Cars:
2004 Gallardo
2004 996 GT3
1999 Viper GTS
1997 993TT
1994 965 Turbo 3.6
1978 930
1972 916
1970 914-6