Grunted adverbs are provided in this article. The words listed here are commonly found along with the verb grunted in sentences. This reference page helps answer the question what are some adverbs that describe or modify the verb GRUNTED.
loudly
merely
noncommittally
simply
softly
Hope this word list had the grunted adverb you were looking for. In addition to adverbs used with grunted, other example verb adverb pairings can be found on this site.
You can help by adding more adverbs in the comments. Thanks.