On My MTD Grendel 4 it seems to have gotten some strange neck warp. Around the first four frets the treble(?)(G String side) is dipping down, causing an unevenness of the neck. Near the 5-7th fret it evens out though. The Bass sounds fine but i want to know if there are any long term problems. On a side note, when changing strings is it safe to take them all off at once and then back on, or should I do them one at a time - like take off E, put on new E etc.