Renault Megane 1.4 1998?

When i go through my first 2 gears and i come to the end of the rev i get a loudish grinding noise, also going down the motorway at 70-ish i get loud engine noise inside the car and need to turn the radio pretty loud to eliminate this. Also the sensor on the central locking is faulty as i have just changed the batteries in the key i have to hold the key right up to the sensor for it to lock and open, and have to reset the imobilisor when in the car before starting.... Any ideas on this?