"Why is my device so slow?"に関する回答Your tablet could have contracted a virus. An anti-malware program can be downloaded to detect if your device has a virus. If it finds a virus, then the program will give a procedure to fix it. If this doesn’t help, then googling the particular virus will likely provide information for further action.
"Why is the sound muffled?"に関する回答Ensure the protective case does not block the speakers. Debris around the speaker areas can cause a distorted sound. If any exists, clean it and listen for a clearer sound quality.