A Lynnfield, Mass. man told Coakley's office that he was being charged premiums from 2003-2008 as if his 1999 Harley-Davidson motorcycle was new and still worth $20,000. By 2008 his motorcycle was worth less than $12,000. Therefore, he was being significantly overcharged because his insurer continued to use the $20,000 value to rate his policy.

An investigation revealed many insurers were doing the same thing.

“We are very concerned that the auto insurers in this state were able to overcharge so many Massachusetts consumers on such a large scale,” Coakley says in a statement.

Her office reached rebate agreements with a dozen insurers last year. With the three newest agreements, motorcycle owners in Massachusetts have been refunded nearly $40 million.

Travelers' Premier Insurance Co., Fireman's Fund subsidiary American Automobile Insurance Co., and Electric Insurance Co will be writing a total of 14,000 rebate checks late this month for an average of $400 under the terms of the latest agreement, says Coakley's office.

Refunds from Premier make up the bulk of the latest settlement. The insurer will write refund checks totaling slightly more than $5 million.

Last year Safety Insurance Group agreed to return approximately $7.2 million to motorcycle policyholders and it affected the company's fourth-quarter income that year.

Also in 2010, the state attorney general's office reached settlement agreements with Liberty Mutual, Quincy Mutual, Metropolitan Property & Casualty Insurance Co., Plymouth Rock Assurance, Pilgrim Insurance Co., United Services Automobile Association (USAA), Arbella Mutual Insurance Co., Hanover Insurance Group, OneBeacon Insurance, National Grange Mutual and Norfolk & Dedham Group.