The environmentalists are more concerned if u break a branch or disturb dirt or water than a loud exhaust.
Having just come out of yet another USFS Stakeholder meeting -- which means I had to sit across the table from Winter Wildlands Alliance, Snowlands Network, Wilderness Society, etc-- with the USFS regarding the OSV travel management plan for the Tahoe National forest, I can tell you that "quiet recreation" is the new battle cry of the non-motorized community.
Loud exhaust is their number one complaint because it is arbitrary and easy for them to say it disturbs their "experience".
In the last 5 years, I have spent hundreds (yes, hundreds) of hours in USFS meetings, driving hours one way to neighboring Forest meetings, and at home preparing maps, counter arguments, and defending the rights of snowmobilers to recreate on PUBLIC lands.
Snowmobilers are the only user group that gets punished as a group versus the individual offender. Loud cans and riding in closed areas by an INDIVIDUAL can get an area closed to an ENTIRE USER GROUP.
Loud cans contribute to land closures EVERYWHERE in the intermountain west. Loud cans have no place in public lands.
Anyone who tells you otherwise is misinformed.