Can you inherit a heart murmur from your grandparents?

No. Heart murmurs are a sign of heart disease, not a disease per se. Some heart disease have a hereditary component and you could get the abnormal gene from your parents. Visit this site for info: https://www.pennmedicine.org/updates/blogs/heart-and-vascular-blog/2019/january/inherited-heart-diseases

Your question is interesting but is too vague to answer adequately. There are several heart conditions that occur in families such as a bicuspid aortic valve, myxomatous mitral valve, hypertrophic cardiomyopathy etc. These are well known examples, but do not answer your question since murmurs are common with ageing and are not necessarily passed on.