The Maryland Department of Natural Resources is seeking tighter restrictions on speed boat noise in two popular boating areas. The agency held a hearing in Elkton on boat noise levels in the northeastern Chesapeake Bay. The limit could be reduced from the existing statewide standard of 90 decibels to 88 decibels for engines made after January 1993. Older boats would still be subject to the 90-decibel rule. Another proposed regulation would prohibit cut-off switches that bypass or reduce the effectiveness of exhaust-pipe mufflers.