As RIM’s decline continues, rumors that rivals are waiting to pick apart the company for patents – like vultures on dead prey – continue to get more fervent. First, in December, the Wall Street Journal reported that a joint Microsoft-Nokia-RIM deal could possibly be in the works. Then, in January, reports emerged that Samsung was taking a long, hard look at RIM. Now, an authoritative source has told Benzinga that Microsoft is preparing to make a serious investment in RIM in exchange for patents.

Microsoft (NASDAQ: MSFT)is prepared to make a $3.5 billion investment in Research in Motion (NASDAQ: RIMM), according to sources. The two companies have been frequently mentioned in potential deals over the past few months.

AOL’s announced sale of 800 patents to Microsoft on Monday, raised interest in RIMM’s patent portfolio.

A Research in Motion spokesperson would not comment on the rumor. A Microsoft spokesperson was not aware of the rumor.

While this potential Microsoft deal with RIM could be dismissed as another RIM rumor, the potential for validity here is greater than with previous speculation: RIM’s share price wont stop its great decline, and new CEO Thorsten Heins has publicly made it clear that “all options are on the table”.

However, some analysts have speculated whether RIM has enough inherent value to warrant a large investment or takeover. Forbes recently reported that one analyst from Sterne Agee has concluded “$1 billion to $1.5 billion” might be a more realistic valuation for RIM’s patent portfolio.

Alternatively, it could just be that this speculation is an elaborate false-flag operation by RIM designed to create small spikes in the company’s share price.

RIM is up 12 cents at $13.05 in Wednesday trading.