I've got the same issues with the water noise (and hard start with rough idling). Noticed that the A/C would stop working because the car is overheating (computer turns off the AC to reduce strain on the engine). I also notice coolant was missing out of the overflow bottle.

Ok, so coolant is a closed system, so the water is going somewhere. Either it is leaking, or getting into the engine. I took it to firestone and they checked it for leaks (none). So the head gasket is leaking (but not into the oil, otherwise it would be milky). I bought some stop leak at napa and used it. Let the car sit for 24 hours. Now the hard start issue is fixed, but the car still overheats. I'm no longer losing coolant though. I haven't bled the system but that shouldn't be difficult. I'll try that next and let you know.

I began hearing the water noise behind the dash at around 50K miles. First I was told it was an air pocket but after havig the system bled it was still there. Then I was told I had a cracked radiator... luckily this was covered under the extended warranty and only cost me $50. Now again at about 78K miles I have the noise again. I called the dealership and was told to bring it in on Monday (I called Thursday) because it was air an air pocket again and the guy said this was common in these cars. Well whaddya know, Friday morning the radiator blew. I had to have the car towed into the dealership and they wanted $1300!!!! My husband screamed and we got the radiator for free but had to pay $200 labor to put it in and another $550 to replace some thermostats in the cooling system that they said was the cause of the radiator overheating. They said this was normal "wear and Tear". I'm certainly no mechanic but 3 radiators in 4 years does not sound right to me. Now it's Monday, everything has been replaced and I still hear the water noise. These cars have problems, I have found many people on many websites with the same issues. If you have had these problems, please contact me at aprncess@earthlink.net... Nissan can ignore us individually but not in large numbers. I am working on learning how to file a class action lawsuit.. thx for your time - Leslie

I am bringing the car in for the THIRD time tomorrow morning. First time they thought I was nuts, second time they said it was low on coolant and filled it and charged me $85.00 and said they then didn't hear the nose... I have since gone through 2 bottle of antifreeze and the sound is still there... so I called today and told them and now that's it's off warranty because of age not miles, I'm sure it will turn into a big problem that they can now fix... I don't intend on paying a penny for this work, we shall see what happens...!!!