Teeth Whitening Options for a Teeth Grinder?

You can and should use custom trays for whitening your teeth.  It is safe and cost effective.  It will not interfere with you wearing your nightgaurd.  Continue to wear your nightgaurd at night, and you can whiten your teeth with the trays during the day.  You should never sleep with bleach trays.  These trays are to be worn during the day for 30-60 minutes, depending on the strength of professional whitening get being used in them.  In office whitening will not whiten your teeth in one visit.  In my opinion it is not worth the money.  See your dentist for custom trays and professional strength whitening gel.

Do not stop wearing your night guard. Many patients who severely grind wear off the top of the enamel of their teeth causing them to darken and become sensitive.
We can zoom your teeth in a two hour visit or take moulds of your teeth and fabricate trays for you to use one hour per day at home: Remember bleaching works best on clean teeth so please visit your dentist to get the best results.

You have better to wear your trays at the day, not at sleep. By clenching the enamel layer of your teeth gets thinner and you are at risk of sensitivity. So contact your dentist if you have any pain or sensitivity to cold.

Whitening trays can and should be worn during the day. It is difficult to monitor tooth sensitivity while sleeping and as such whitening trays should be worn during the day to prevent over use and sensitivity. In your particular case this should not interfere with your night guard use.

Actually, you can do teeth whitening with trays! Ask about custom trays from your dentist.
You dont need to wear whitening trays at night because most bleaching gels (provided by dentists) are ineffective after max 45 minutes. You can use the trays anytime during the day. At night, you can wear your nightguard. Your problem is solved.
There are also other options. Modern techniques allow for in-office bleaching in 30 minutes.
Good luck.

If you use trays during the day and not at night, you should be able to get the result you are looking for without sacrificing night guard wear.  It may be for shorter times, so it may take longer than the normal 2 weeks to get them as white as they will get.

Some of the newer tray style bleach systems only need to be worn 2 hrs. Most people wear these between dinner and bedtime. Since you are a clencher you may experience some sensitivity. Alternating a flouride gel in the tray with bleach everyother night usually helps.