CRJ900 Captain reports strange slapping noise apparently coming from outside the aircraft just after takeoff. The flight returns to discover speed tape wrapped around the base of the Captain's pitot tube.

Narrative

After a normal takeoff and shortly after being handed off to Departure Control; the First Officer; off line jumpseater; and myself heard a strange noise coming from outside the left of the flight deck. The noise sounded like someone was taking a strap and beating it alongside the fuselage just below the Captain's side window. My first reaction or thought was that either the pitot tube or ice detect system had become detached from its base and was dangling and hitting the fuselage thus making that noise but all indications that receive information from these probes were operating normal thus making us curious to what it was. As a result of the continuous noise we decided to return for a precautionary landing and had notified Dispatch and Maintenance of the situation. We determined that we were overweight so we burned about 20 minutes of fuel as to make the landing just under 75;100 lbs. We notified ATC of the noise and our intentions and made a decision that it was not an emergency and told ATC that we were NOT declaring an emergency several times; once to Approach Control and the other to the Tower. Somehow in the mix however; ATC apparently was misinformed and treated our situation as an emergency. We landed without incident and taxied to the gate. As we approached our gate maintenance noticed a piece of speed tape wrapped around our primary pitot tube and thus removed it and checked the condition of the tube. The tube was in good condition and the tape was found to not have impeded its function (it was only wrapped around its base). The aircraft was found airworthy and we took on more fuel at the gate and departed again without incident. Where the tape came from was not determined.