OTTAWA -- The Senate board of internal economy has issued a report saying it has no issue with the housing allowances of all but three senators.

An investigation was started last month after revelations that three long-time Ottawa residents in the upper chamber were improperly claiming allowances meant to compensate senators who keep a secondary residence in the national capital region.

All 98 sitting senators were asked for documentation by the internal committee, which reviewed their driver's licences, health cards and residency information on their income tax returns.

As a result of the document checks, two senators, Dennis Patterson and Rod Zimmer, were interviewed by the committee but subsequently cleared.

External auditors continue to look at the expenses of Conservative Sen. Mike Duffy, Liberal Mac Harb and Sen. Patrick Brazeau, who was turfed from the Conservative caucus this month on an unrelated criminal matter.

Auditors are also examining the travel expense claims of Conservative Sen. Pamela Wallin.

Duffy has volunteered to repay his $22,000-per-year allowance; Wallin has not denied reports she has repaid a substantial chunk of her travel expenses, which total $321,000 since September 2010.